1. Field of the Invention
The present invention relates to an infrared sensor and an infrared sensor module.
2. Description of the Related Art
Hitherto, an infrared sensor using, as a sensing unit, an element (thermopile) that generates voltage when heat is applied is known (refer to Japanese Patent Application Laid-Open Nos. H06-229821, H11-258038, H11-258040, H11-258041, 2000-65639, 2000-221080, and 2000-292254). The thermopile receives infrared light emitted from an object and, when a temperature difference occurs, generates a voltage difference corresponding to the temperature difference due to the so-called Seebeck effect. By detecting the voltage difference as a function of the temperature change, the temperature of an object can be sensed.
Such an infrared sensor is used as a sensor module in which a plurality of sensing units is arranged in the vertical and horizontal directions (in an array) in a vacuum-sealed case in order to suppress deterioration in sensitivity caused by dispersion of heat into air.
Each of the sensing units receives infrared light incident from an infrared transmission window (infrared filter) formed in the case and outputs voltage. Since an output signal from the sensing unit is small, it is amplified or integrated by an arithmetic circuit or the like.
However, a conventional infrared sensor has a configuration such that the arithmetic circuit is mounted in a position apart from the sensing unit, and noise tends to occur in the output signal from the sensing unit. For miniaturization of the sensor, the conventional infrared sensor is constructed to process output signals of all of the sensing units in the sensor array by one or a few arithmetic circuits. By connecting the plurality of sensing units to one arithmetic circuit, the sampling frequency be comes high, and it causes noise.
Japanese Patent Application Laid-Open No. 2007-313594 discloses a stacked device directed to reduce the size of a chip and shorten interconnection by stacking the sensor unit and the arithmetic circuit. However, in an infrared sensor so configured, heat (infrared light) generated by the arithmetic circuit may cause noise in the infrared sensor.
Moreover, a work of mounting the sensing units in the vacuum-sealed case includes a complicated work such as degasifying work, and expensive parts, special adhesive, and the like are necessary for the case requested to have high air tightness. Therefore, the conventional configuration in which the sensing units are housed in the vacuum-sealed case has a problem also from the viewpoint of manufacture cost.